Explained: Yale’s Saliva-based COVID-19 Test That Promises Rapid Detection Of Coronavirus At Low Cost

Large-scale, rapid testing to detect coronavirus infections is critical in the pandemic.

Catching an infection early can help in containing the spread of the virus, prevent late-stage illness and, consequently, help save lives, and pave the way for a safe reopening of society, including but not limited to restarting of schools and colleges, workplaces, and commercial establishments.

Detecting the novel coronavirus SARS-CoV-2 has involved the reverse transcription polymerase chain reaction test, abbreviated to a less intimidating “RT-PCR” test, with a sample collected from the back of a person's nose or mouth.

You may have seen it in pictures if not gone through it yourself. Nasopharyngeal swabbing is more unpleasant than it looks. It was chosen as the preferred sampling technique because of prior diagnostic experience dealing with respiratory infections.

But despite its unpleasantness and other challenges, countries have been using it and gradually increasing their testing numbers.

However, there is a limit to how much COVID-19 testing can be ramped up with this technique. The logistics is definitely a barrier – because of the specific requirements for swabbing – and it doesn’t help that supply chain issues sometimes cause disruption in procuring the material necessary.

Stepping up testing numbers requires a method that is quicker, cheaper, more amenable (children and elderly shouldn’t have it this hard), widely available, and greatly accessible.

A new technique devised by researchers at the Yale School of Public Health promises exactly that.

The novel idea involves changing how the sample is taken. Instead of digging into the back of the nose or mouth, a saliva sample is instead collected for testing. For this, one only has to reach the tongue.

SalivaDirect, the name for this technique, simplifies sample collection, enables frequent sampling, and doesn’t require skilled health workers for collecting the sample.

Research indicates that the technique is highly sensitive and produces outcomes similar to the nasopharyngeal swab test.

It received emergency-use authorisation by the United States Food and Drug Administration (FDA), Yale University announced this last Saturday (15 August).

The approval essentially gives American laboratories the green signal to go ahead and adopt this technique if they wish to (details for labs here) after acquiring proper accreditation.

The potential of saliva use to expand testing for SARS-CoV-2 was identified earlier in spring, thanks to efforts led by Yale researchers Nathan Grubaugh and Anne Wyllie. Since then, the improvements have been made to the method with a focus on cutting cost and time.

The scientists explain in their paper how they reduced the cost: “Saliva does not require a certified swab and collection receptacle and does not necessarily have to be obtained by a skilled healthcare provider, both of which increase diagnostic associated costs.”

According to the researchers, the cost per sample could be as low as $1.29 (Rs 97) to a high of $4.37 (Rs 328), with the addition of a saliva collection aid.

At its low cost, SalivaDirect still registers a 94 per cent agreement with nasopharyngeal swabs in COVID-19 tests.

Extracting nucleic acid from samples – a key part of the nasopharyngeal swab tests and which takes time and is expensive – doesn’t feature in the SalivaDirect method. This cuts down delays that sometimes occur on account of supply shortages in the material required for the extraction.

The saliva-based technique instead incorporates the addition of a reagent and a brief heating phase. The team tried out several commonly used reagents (they were mixed with the saliva sample) and obtained successful results. Therefore, labs equipped to do this work could conduct this test without hassle.

The saliva-based test is safer, too. In the traditional method, the insertion of a swab into the back of the nares can induce a cough or sneeze and, therefore, an ejection of droplets from persons suspected of carrying the virus. Collecting saliva potentially lowers that risk, especially if the sample is self-collected under the supervision of a healthcare professional.

There is just one condition at the moment for using this technique. The sample collected should be clear and liquid saliva. Therefore, SalivaDirect cannot be used on hospitalised COVID-19 patients since their saliva samples could carry blood or mucus, affecting the eventual reading.

Yale researchers have revealed that they don’t plan to rest now that the emergency-use approval has been granted by the US FDA. They plan to pursue certain improvements in order to keep cutting away at time and cost.

Some of the directions that they plan to take are the use of robots for sample processing and/or PCR, pooling in saliva from many people and testing it all at once, and pursuing alternative approaches to PCR.

The second and third of these three current and future steps would enable more testing per day and faster testing per sample.

One of the important aspects of COVID-19 testing as we progress in the pandemic is identifying the presence of the virus in asymptomatic individuals. That seems to be a focus of the Yale researchers. Players and staff from the National Basketball Association (NBA) are participating in a trial to determine if the saliva-based test can detect infection accurately in people who don’t show symptoms. Testing with samples drawn using the conventional nasal/oral technique will be done in parallel so as to compare the results after completion of the trial.

The NBA has also been funding the SalivaDirect research along with the National Basketball Players Association. They have pooled in $500,000, reports ESPN.

Yale is at work now to make the test accessible to more people with the help of the Connecticut-based Jackson Laboratory for Genomic Medicine.

The Yale scientists have said that they don’t aim to profit from this technique and are singularly committed to increasing daily rapid COVID-19 testing. So, there will be no “SalivaDirect kit” to buy, and the “open source” protocol is free to be adopted and even modified by other groups for improvements.

The US FDA revealed that SalivaDirect is the fifth saliva-based test that it has authorised. Although results from earlier tests based on saliva haven’t always been consistent, the FDA said it found Yale’s test to meet the criteria for emergency authorisation after going through the submitted data.